Weather-proof surface resistant to checking and alligatoring



United States Patent O 3,247,ili1 WEATHER-FROG? SURFACE RESESTANT T CHECKENG AND ALLEGATORHNG William A. Higgins, Cleveland, (thin, assignor to The Lubrizol Corp, Wickliife, Ohio, a corporation of Ghio No Drawing. Filed .luly 6, i961, Ser. No. 122,094 3 Claims. (Cl. 117--92) The present invention relates to an improved weatherproof surface which resists checking and alligatoring. In a more particular sense, it relates to a weather-proof surface such as a root surface in which the residue of a particular kind of aqueous asphalt emulsion is superimposed on a layer of solid bitumen.

Bituminous materials such as petroleum asphalt, Trinadad natural asphalt, gilsonite, unitahite, coal tar, pitch, and the like have long been employed in the manu factnre of weather-proofing and roofing compositions. One common method of making roof surface from a bituminous material involves heating the bitumen, generally a petroleum asphalt, until it is liquid and then applying a layer of the hot, liquid bitumen to the roof structure, i.e., the roof deck. Upon cooling, the bitumen solidifies and forms a protective water-proof layer. A less frequently used method involves applying a liquid asphalt cut-back (a solution of asphalt in a volatile solvent such as petroleum mineral spirits) to the roof deck. Upon evaporation of the solvent, a solid layer of the bitumen remains. Similar methods, especially the latter method, are followed in providing a protective, weather-proof surface for structures such as, e.g., steel storage tanks, steel bridges, and the like.

The roof deck to which the bitumen is applied ordinarily consists of a wooden substrate covered with roofing felt, i.e., asphalt-impregnated or tar-impregnated paper. The roofing felt supplies a certain amount of water-proofing, compensates for any movement of the wooden substrate, and serves as an excellent base to receive the top coat of liquid bitumen. In recent years, slabs of prestressed concrete or monolithic concrete shells have gained in popularity as roof decks. The conventional manner of water-proofing such concrete roof decks is to apply first a thin layer of hot, liquid bitumen to the concrete surface, then lay down the roofing felts, :and finally apply a top coat of hot, liquid bitumen. It is estimated that at least 80% of all factories and commercial buildings in the United States have roof surfaces of one or the other of the two general types described above.

Although bitumen covered roofs have gained wide acceptance by reason of their initial low cost and relative ease of construction, they have certain serious shortcomings. A principal shortcoming is their relatively high maintenance cost. After a year or so of exposure to weather (the exact time varies with the severity of the climate but is generally not more than 2 years), the layer of bitumen generally develops a multitude of fine cracks. In particularly severe cases these cracks extend from the weather surface of the bitumen to the roof deck and form a pattern similar to that of alligator skin, giving rise to the term known in the roofing art as alligatoring. Severely alligatored roofs are not waterproof and require prompt repair if damage to the roof deck and building contents is to be avoided. Depending on the extent of alligatoring, the repair usually involves either the application of an asphalt cut-back to the damaged roof surface or a complete resurfacing of the roof with hot, liquid bitumen. The renewed roof surface is likewise susceptible to cracking and alligatoring and may require attention again in a few years. Thus, over a period of many years of successive applications of asphalt cut-back and/or hot, liquid bitumen, the

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weight of bitumen which must be supported by the roof deck is significantly increased and may, in the case of large roof areas, call for additional roof deck bracing.

Another disadvantage of bitumen covered roofs is related to their high absorption of infrared rays. A black layer of bitumen develops high temperatures, often reaching 160 F., when exposed to intense sunlight. The heat radiates in part to the interior of the building, where it contributes to the discomfort of the occupants or constitutes an additional load on air-conditioning equipment. In addition, the bitumen may become sufliciently hot to undergo plastic flow, which in the case of an inclined roof causes rippling and. over along period acts to thin out the uppermost layers of bitumen and build up heavy layers of bitumen on the lower portion of the roof.

Still another disadvantage of bitumen covered roofs is their lack of decorative value. The jet black appearance of a bitumen covered roof is considered objectionable by many architects when the building design calls for large areas of inclined roof surface which are visible from the ground. In such instances the bitumen is usually surfaced while yet molten with a layer of fine slag, gravel, white marble chips, or colored marble chips to provide a more attractive roof surface. Surfacing operations of this kind are not only inconvenient but the mineral employed contributes materially to the weight which must be borne by the roof deck and its supporting structure.

It is an object of this invention to provide an improved weather-proof surface which resists checking and alligatoring.

Another object is to provide a thermally stable roof surface which resists plastic flow.

Another object is to provide a decorative, gray roof surface of good reflectivity.

Still another object is to provide a convenient and economical process for preparing an improved weatherproof surface.

These and other objects are achieved according to the present invention by a process which comprises (a) applying a layer of liquid bitumen to a structure, (b) allowing said layer of bitumen to solidify, and (c) applying a layed of an aqueous asphalt emulsion containing as essential ingredients water, asphalt, clay, and titanium dioxide over said layer of solidified bitumen.

The liquid bitumen of (a) is generally a molten asphalt or an asphalt cut-back. Of the various known naturallyoccurring and manufactured asphalts which can be used, petroleum asphalt (i.e., the residue from the refining of crude petroleum) is preferred by reason of its low cost, avaiiability, and excellent water-proofing characteristics. A particular preference is expressed for high melting petroleum asphalts such as those which have a ringandball softening point within the range of from about to about 250 F. as determined by ASTM test 1336-26. Asphalts within this range are less susceptible to plastic flow on a surface exposed to weather than are the lower melting asphalts, and yet are not so difiicultly fusible or soluble as to pose problems with respect to their liquefaction and application to a structure such as a roof deck, a storage tank, or a bridge.

The aqueous asphalt emulsion of (c) preferably contains fillers or extenders for the characterizing white titanium dioxide pigment. A mixture of finely-divided talc, mica, and diatomaceous earth has been found to be very effective for this purpose and to reduce substantially the amount of the relatively expensive titanium dioxide which otherwise would have to be used to achieve the desired gray colored emulsion. For best results, the talc, mica, and diatomaceous earth should be in the form of pigment grade powders.

The asphalt used in preparing the emulsion may be either a naturally-occurring asphalt or a manufactured asphalt such as petroleum asphalt. For the reasons adduced earlier, a petroleum asphalt is generally preferred. A relatively soft petroleum asphalt having a penetration value Within the range from about 40 to about 100 as determined by ASTM test D-52 has been found to emulsify readily with Water, clay, and titanium dioxide, and is particularly preferred for the purpose of the present invention.

The clay ingredient of the emulsion may be any one of several clays such as, e.g., kaolinite, anauxite, attapulgite nacrite, china-clay, or bentonite. By reason of its commercial availability, low cost, and ease of emulsification, bentonite is usually preferred. The state of division of the dry clay appears to be of no consequence; powered and granular forms have been employed with equal success.

The titanium dioxide ingredient is generally either the mineral rutile or anatase reduced to a fine powder by grinding or ball-milling. Commercial, pigment-grade rutile is very satisfactory as this ingredient.

The aqueous asphalt emulsion employed for the purpose of this invention contains as essential ingredients from about 20 to about 80 parts of water, from about to about 30 parts of asphalt, from about 20 to about 30 parts of titanium dioxide and from about 0.5 to about 5 parts of clay, all parts being by weight. The amount of titanium dioxide required can be reduced to about 5 to about parts by employing a low cost pigment extender mixture consisting of from about 1 to about 5 parts of powdered mica and from about 2 to about 10 parts each of powdered talc and diatomaceous earth. The preferred emulsion contains as essential ingredients about 45 to 60 parts of water, about to parts of petroleum asphalt having a penetration value of from about 50 to about 100 as determined by ASTM test D5-52, about 1 to 2 parts of bentonite, about 8 to 12 parts of titanium dioxide, about 2 to 3 parts of mica, and about 4 to 6 parts each of talc and diatomaceous earth.

It should be noted that upon drying (i.e., evaporation of Water therefrom), these emulsions yield a heterogeneous asphaltic composition containing the several solid, non-volatile ingredients in the same relative proportions that exist in the original emulsion.

To facilitate the compounding of the emulsion, small amounts of auxiliary materials such as buffering agents, flocculating agents, foam inhibitors, and dispersing agents may also be employed. Suitable buffers include alkali metal dichromates, mineral acids, and low molecular weight carboxylic acids such as, e.g., potassium dichromate, sodium dichromate, hydrochloric acid, acetic acid, and propionic acid.

The water-soluble, heavy metal sulfates, particularly cupric sulfate, are useful as fiocculating agents and the polymerized dialkyl silicones are effective in controlling excessive foaming during preparation of the emulsion. The foam inhibiting properties of silicones are wellknown and a number of such products, known in the trade as silicone fluids, are available commercially.

Wetting and dispersing agents which are useful in stabilizing and adjusting the viscosity of the emulsion include, for example, the alkali metal sulfonates such as, e.g., sodium mahogany sulfonates; the alkali metal mono-alkyl sulfates such as e.g., sodium mono-lauryl sulfate; and the sodium salt of a carboxylated polyelectrolyte available commercially under the designation Tamol 731. The latter material is particularly effective in the emulsions used in the process of this invention.

If desired, a fungicide such as phenyl mercuric acetate may also be added to the emulsion to inhibit mildewing of the heterogeneous asphaltic residue of asphalt, clay, pigment and optionally, pigment extenders which remains after the emulsion has been applied to a layer of bitumen and the water has evaporated therefrom.

The compounding of the aqueous asphalt emulsion required in the practice of the present invention may be carried out conveniently as follows:

The clay is hydrated with approximately one-half the total amount of Water to be present in the final emulsion. Buffering and/or flocculating agents, if employed, are then added to the water-clay slurry, and the whole is intimately mixed with the titanium dioxide pigment and, optionally, any pigment extenders. Additional water in an amount up to about one-fourth the total amount is added as required during this blending operation to assure complete hydration of the pigment and extenders and to prevent dry spots. An anti-foam agent is added, if desired, and the whole is then heated to a temperature within the range of from about F. to about F. While the pigmented slurry is being thoroughly mixed, the molten asphalt (250350 F.) is added slowly together with most of the remaining water. After all the asphalt has been dispersed, the last remaining portion of water and, optionally, a wetting agent are added to adjust the viscosity of the final emulsion so that it brushes well.

In the ordinary practice of the invention as it relates to a completely new roof surface, a layer of the molten bitumen, preferably petroleum asphalt, is brushed or mopped on the roof deck and then allowed to cool and solidify. Sufficient bitumen is used to yield a layer having an average thickness within the range of from about 10 to about 100 mils.

After the bitumen has solidified, a layer of the aqueous asphalt emulsion containing as essential ingredients water, asphalt, clay, and titanium dioxide is applied by any suitable technique such as brushing, mopping, spraying, or roller-coating. Sufficient emulsion is used to yield a layer having an average thickness, while wet, of from about 5 to about 30 mils. After the water has evaporated from the emulsion, the heterogeneous asphaltic residue thereof becomes firmly bonded to the bitumen in the form of a layer having an average thickness between about 2.5 and about 15 mils.

Normally the application of the bitumen and the subsequent application of the aqueous asphalt emulsion take place within a few days of one another; however, bitumen covered roofs and steel storage tanks several months or even several years old have been treated with the aqueous asphalt emulsion required for the process of this invention. Thus it will be understood that the layer of bitumen contemplated for the purpose of this invention can represent the bitumen deposited on a structure from one, two, three, or more applications of hot, liquid bitumen and/or asphalt cut-back. Likewise, the layer of bitumen may be new and crack-free or weathered and even alligatored.

The weather-proof surface of this invention, i.e., the layer of bitumen covered with a layer of a heterogeneous asphaltic residue containing as essential ingredients asphalt, clay, and titanium dioxide, has a pleasing, gray color. After two and one-half years exposure to the weather prevailing in the Great Lakes region, it has shown no evidence whatever of plastic flow, checking, or alligatoring. Furthermore, it has shown a body temperature 20 F. lower than that of a layer of conventional, hot-mop asphalt on a sunny day, indicative of its good reflectivity.

The following examples are submitted to set forth specific modes of carrying out the present invention. They are intended only for purposes of illustration and are not to be construed as limiting the scope of the invention.

Example 1 An aqueous asphalt emulsion of the type required for the present invention is prepared as follows (all parts are by weight):

450 parts of powdered bentonite is slurried in 5,550 parts of water and while the whole is stirred thoroughly, 21.4 parts of a 16% aqueous solution of equal parts of;

potassium dichromate and glacial acetic acid, 6.9 parts of glacial acetic acid and 48.7 parts of a aqueous solution of cupric sulfate are added as buffering and flocculatiug agents. 2900 parts of finely powdered, pigment-grade rutile is then added slowly. After all of the rutile has been added and thoroughly dispersed in the clay slurry (check for dry spots), 1,125 parts of powdered, paint-grade tale is added, followed by 1,390 parts of water. The whole is stirred for about minutes, and then 705 parts of 325-mesh mica powder, 1,280 parts of commercial, paint-grade diatomaceous earth, and

Roof Section Inspection after 1 month 2 months 9 months 2 years rippled. Control (hot-mop asphalt). No cracks; slight rippling.

No cracks; no plastic flow deeper rippling.

Same condition as at 1 mo- Cracks became wider and No cracks; moderate Same condition as at 1 mo Same condition as at 1 mo.

No cracks; pronounced N 0 cracks; very heavy rippling. rippling.

Slightly alligatored Heavily alligatored.

1 No inspection recorded because roof surface was considered completely unsuitable at the 2-month inspection.

890 parts of water are added slowly in the stated order. To reduce foaming, 71 parts of a 2% aqueous dispersion of a commercial silicone fluid is also added.

The thus prepared aqueous pigmented slurry is stirred and warmed to about 100 F. 6000 parts of molten (265-275 F.) petroleum asphalt having a penetration value of about 60 according to ASTM test D552 is added slowly. Simultaneously with the addition of the asphalt, 6000 parts of water is also added via a separate feed line. During the blending of the pigmented slurry, asphalt, and water, the temperature of the mixture is maintained between 110 and 120 F. by cooling or heating as required.

After the asphalt has been emulsified in the aqueous pigmented slurry, 1050 parts of a 3% aqueous solution of phenyl mercuric acetate (a fungicide) and 12 parts of Tamol 731 (a wetting agent) are added. A final addition of water is then made (varying from about 100 parts to about 1000 parts, generally about 700 parts) to adjust the viscosity of the finished emulsion so that it brushes well. The finished emulsion has a pleasing, gray color and a density of about 9.8 lbs. per gallon.

Example 2 An emulsion is prepared according to the procedure given in Example 1, except that 5000 parts of pigmentgrade rutile is used in lieu of the specified amounts of rutile and pigment extenders (talc, mica, and diatomaceous earth). The amounts of water accompanying the addition of the pigment extenders in Example 1 are added, in this instance, during the addition of the rutile.

Example 3 A SO-mil thick layer of hot-mop petroleum asphalt (147 F. ring-and-ball softening point, ASTM D3626) was applied to an inclined (8 from horizontal) roof deck consisting of a concrete substrate covered with roofing felt. After the bitumen had weathered for one week, three adjacent 1 x 2.5-foot sections thereof were treated as follows:

Section A.Two coats of the emulsion of Example 1 were brushed on the roof section to yield a layer having a wet thickness of about 20 mils. After evaporation of the water from the emulsion (ca. 8 hours required), the gray, heterogeneous asphaltic residue deposited on the bitumen had an average thickness of 10 mils. This section constitutes a roof surface of the present invention.

Section B.Two coats of a commercial aqueous asphalt-clay roofing emulsion containing asphalt, water,

What is claimed is:

1. An article comprising a structure having thereon a weather-proof coating resistant to checking and alligatoring which comprises (a) a layer of bitumen having superimposed thereon (b) a layer of an asphaltic composition applied to the structure as an asphalt emulsion containing as essential ingredients from about 20 to about parts of water, from about 10 to about 30 parts of asphalt, from about 0.5 to about 5 parts of clay, and from about 5 to about 15 parts of titanium dioxide.

2. An article comprising a structure having thereon a weather-proof coating resistant to checking and alligatoring which comprises (a) a layer of petroleum asphalt having superimposed thereon (b) a layer of an asphaltic composition applied to the structure as an asphalt emulsion containing as essential ingredients from about 20 to 80 parts of Water, from about 10 to about 30 parts of petroleum asphalt, from about 0.5 to about 5 parts of bentonite, from about 5 to about 15 parts of titanium dioxide, from about 1 to about 5 parts of mica, and from about 2 to about 10 parts each of talc and diatornaceous earth.

3. An article comprising a structure having thereon a weather-proof coating resistant to checking and alligatoring which comprises (a) a layer of petroleum asphalt having a ring-and-ball softening point of from about 140 to about 250 F. as determined by ASTM test D36- 26 having superimposed thereon (b) a layer of an asphaltic composition applied to the structure as an asphalt emulsion containing as essential ingredients from about 45 to about 60 parts of water, from about 20 to 25 parts of petroleum asphalt having a penetration value of from about 40 to about as determined by ASTM test D5-52, about 1 to 2 parts of bentonite, about 8 to 12 parts of titanium dioxide, about 2 to 3 parts of mica, and about 4 to 6 parts each of talc and diatomaceous earth.

References Cited by the Examiner UNITED STATES PATENTS 1,448,155 3/1923 Schutte 11732 2,332,311 10/1943 Fadden 106283 X 2,400,563 5/1946 Mark 106281 2,481,370 9/ 1949 Vanden Berge 117--92 2,721,146 10/1955 Hardrnan 11792 2,733,159 1/1956 Scoggin 106-283 X 2,858,231 10/1958 Watson 11772 X WILLIAM D. MARTIN, Primary Examiner.

RICHARD D. NEVIUS, Examiner. 

1. AN ARTICLE COMPRISING A STRUCTURE HAVING THEREON A WEATHER-PROOF COATING RESISTANT TO CHECKING AND ALLIGATORING WHICH COMPRISES (A) A LAYER OF TIBUMEN HAVING SUPERIMPOSED THEREON (B) A LAYER OF AN ASPHALTIC COMPOSITION APPLIED TO THE STRUCTURE AS AN ASPHALT EMULSION CONTAINING AS ESSENTIAL INGREDIENTS FROM ABOUT 20 TO ABOUT 80 PARTS OF WATER, FROM ABOUT 10 TO ABOUT 30 PARTS OF ASPHALT, FROM ABOUT 0.5 TO ABOUT 5 PARTS OF CLAY, AND FROM ABOUT 5 TO ABOUT 15 PARTS OF TITANIUM DIOXIDE. 